Hygiene flushing: how long and how often to flush?

A hygiene flush is an automatic exchange of the water at a outlet, replacing the standing water before Legionella can multiply. During a hygiene flush, a complete water exchange is required at least every 72 hours. You flush until the temperature holds steady, meaning the stagnant water has been fully pushed out. Depending on the pipe volume, this takes between about 30 seconds and several minutes per outlet.

At a glance

  • Water exchange at the latest every 72 hours per outlet (VDI 6023 Part 1, proper operation)
  • Flush until temperature stability, outlet fully open
  • Exchange cold and hot water separately
  • Over 7 days of stagnation: complete water exchange in accordance with DVGW W 551-3, over 4 weeks also a microbiological follow-up test
  • Duty to operate at least in accordance with the generally accepted rules of technology (§ 13 TrinkwV 2023)
Water flowing from a shower, a symbol of regular water exchange
Regular water exchange keeps the system in proper operation and prevents stagnation.

How often is a hygiene flush needed?

Under VDI 6023 Part 1, going more than 72 hours without a water exchange counts as an interruption of operation. The interval applies per outlet, not per building: a shower that has not been used for four days is due, even if the building is well occupied.

How long do you need to flush?

Which measure is due depends on how long the water has been standing. The following classification summarises what to do from each stagnation duration onward:

Classification based on VDI 3810 Part 2 / VDI 6023 Part 3 (Table 2), DIN EN 806-5 and DVGW worksheet W 551-3 (A). Own illustration.

Temperature constancy means that the water at the outlet has reached the same temperature as the fresh water in the supply line. Cold and hot water must be considered separately: cold until it stays reliably cold, hot until it comes out hot.

Why the outlet must be fully open

VDI 6023 Part 1 requires a turbulent flow for stagnation flushing. A half-open tap does not reach that flow rate, and the water is not completely exchanged. In large or sprawling systems, several outlets must run at the same time to cover the distribution pipes.

In which order do you flush?

As a rule, you flush from the supply line outward to the most distant outlet, so that fresh water passes through the entire network. Cold and hot water are handled separately. With several risers, you start at the point closest to the building connection and work your way toward the peripheral outlets.

What matters is that every single outlet is actually reached. One forgotten shower is enough to leave a stagnant zone in which Legionella can multiply undisturbed. That is exactly why each outlet has to be logged on its own.

Why manual flushing fails in practice

Without measurement, the end of the flush cannot be identified, so people round up, every day, at every shower. And there is a prior question: which outlet is even due? No occupancy system records when someone last showered.

How Aqvior automates this

Automatic hygiene flushing: what changes

The requirement does not change when the flushing is automatic instead of manual. It remains the same complete water exchange, at the same outlet, on the same interval. What changes is exactly the three places where flushing by hand fails.

A shower is due when nothing has run for 72 hours

Automatic hygiene flushing does not count days on a calendar. It counts the hours since water was last drawn at that one outlet. If no water has run at a shower for 72 hours, it flushes on its own. If someone showers normally, it does not, because that use is already the water exchange.

Because it flushes at 72 hours, the shower never reaches the next stagnation step at all. The steps above apply to outlets where nobody has flushed.

That is the difference that weighs most in a care home and in a hospital. The occupancy list says who lives in a room. It does not say when water last ran there. A resident who is washed at the bedside, a patient who spends three weeks on another ward: the room is occupied and the shower stands still.

The flush is set up, not estimated

We do not simply let water run. The flush is set up for the installation, and the temperature, duration and time are measured and logged for every flush.

The record is written during the flush

Every flush lands in the dashboard: date and time, duration, volume and the temperature. Not a tick on a list, but a measured value per outlet and per event.

The manager has direct access to the dashboard and receives a monthly compliance summary for every connected shower. The records stay available for ten years. See the dashboard

72 hours is the maximum, not the target

Where there are special requirements, as in hospitals and care facilities, shorter intervals are necessary.

What it takes in the building

It is retrofitted without renovating the bathroom, one shower per room, in under an hour. It only flushes when the shower is free. The room can be used again the same day.

What it does not replace

Automatic flushing keeps up, at the shower, the water exchange that intended operation requires. Other outlets keep their own flushing routine. It replaces neither the testing obligation nor the risk assessment once the action level is reached, and it does not correct a system that is run too warm or too cold.

For your facility

The interval applies equally to every facility; the effort differs by type of operation.

Flush without guessing, every flush the same and documented

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Frequently asked questions

Does every hygiene flush have to be documented?

The operator must be able to demonstrate the regular water exchange. That is why each flush is logged per outlet with a date, because without this record the proof cannot be provided in an inspection.

What applies after a longer vacancy or holiday?

After an interruption of operation, the measure depends on the duration of stagnation. Up to three days, flushing until temperature stability is sufficient; from 72 hours to seven days the water has to run for at least five minutes at several outlets at once. For a longer standstill, a complete water exchange in accordance with DVGW W 551-3 is provided for. After more than four weeks, microbiological control tests in cold and hot water are added. In detail: what is due after a longer shutdown.

Does the normal use of a shower already count as flushing?

Yes. If a outlet is used at least every 72 hours, the water exchange counts as met as intended and an additional flush is not needed. If use does not happen, stagnation favours the growth of Legionella.

Who is liable if flushing is not carried out regularly?

The operator of the drinking water installation is responsible and must operate it at least in accordance with the generally accepted rules of technology (§ 13 TrinkwV 2023). If water exchange and flushing are neglected, the operator bears the consequences, for example when the Legionella test shows an exceedance.

Is there a legal obligation to carry out a hygiene flush?

The Drinking Water Ordinance does not name the hygiene flush explicitly, but requires operation at least in accordance with the generally accepted rules of technology (§ 13 TrinkwV 2023). The decisive water exchange every 72 hours under VDI 6023 Part 1 makes regular flushing effectively binding as soon as normal use does not ensure it.

The content of this page is for general information and does not replace legal, technical or health advice in individual cases. Information on Legionella and the associated health risks is general in nature and constitutes neither medical advice nor an assessment of a specific drinking water system. For implementation in your operation, coordinate the specific situation with the responsible health authority.